Steering torque detecting device

ABSTRACT

A steering torque detecting device comprises a steering shaft consisting of an input shaft and an output shaft, a torsion bar provided between the input shaft and the output shaft, a torque detecting unit for converting a quantity of torsion produced in the torsion bar into an electric output, an electricity collecting unit comprising slip rings and brushes which takes the electric output and supplies an electric power from an outer power source, bearings for supporting the input and output shaft on the same axial line, and a housing supporting the bearings, a printed wiring board in a circular plate form which is provided at its one surface with a resistance layer and an output electrode radially spaced apart from the resistance layer, the resistance layer and the output electrode constituting a potentiometer, and a slider having a portion extending in the radial direction of the circular printed wiring board so as to have contacting areas with a small width to the resistance layer and the output electrode.

This is a division, of application Ser. No. 177,085, filed Apr. 4, 1988.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a steering torque detecting device usedfor a motor-driven power steering system installed in, for instance, anautomobile.

2. Discussion of the Background

There has been known a steering torque detecting device of such a typethat a steering shaft is divided into an input shaft and an outputshaft, a torsion bar is provided between the input and output shafts toconnect them, displacement caused by a twisting force in the torsion baris converted into displacement in stroke by means of a displacementconverting means constituted by gears provided between the input andoutput shafts, and the displacement in stroke is detected by a stroketype potentiometer.

There has been known another type of detecting device which is soconstructed that such displacement in the torsion bar is converted intoa rotational displacement by means of a displacement converting meansconstituted by gears, and the rotational displacement is detected by arotation type potentiometer. Thus, a quantity of torque detected is usedto rotate a motor for steering operation so as to correspond to thedetected quantity.

Thus, in the conventional steering torque detecting device utilizing thedisplacement converting means formed of the gears to convert thedisplacement in torsion into the displacement in stroke or thedisplacement in rotation, there is a disadvantage in that the entirestructure is complicated and is large-sized.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a steering torquedetecting device having a simple structure, and which is light weightand of a small size.

The foregoing and the other objects of the present invention have beenattained by providing a steering torque detecting device which comprisesa steering shaft consisting of an input shaft and an output shaft, atorsion bar for connecting the input shaft with the output shaft, aprinted wiring board in a circular plate form which is provided at itsone surface with a resistance layer and an output electrode radiallyspaced apart from the resistance layer, the resistance layer and theoutput electrode constituting a potentiometer, and which is attached toeither the input shaft or the output shaft, a plurality of slip ringswhich are fixed to either shaft and are connected to electrodes formedat both ends of the resistance layer and the output electrodes, aplurality of brushes in contact with the slip rings to receive detectionsignals, and a slider mounted on the other shaft and having a portionextending in the radial direction of the circular printed wiring boardso as to have contacting areas with a small width to the resistancelayer and the output electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the following detailed description when considered inconnection with the accompanying drawings in which like referencecharacters designate like or corresponding parts throughout the severalviews and wherein:

FIG. 1 is a longitudinal cross-sectional view of an embodiment of thesteering torque detecting device according to the present invention;

FIG. 2 is a front view of an embodiment of the printed wiring board usedin the steering torque detecting device according to the presentinvention;

FIG. 3 is a perspective view of an embodiment of the slider used for thesteering torque detecting device as shown in FIG. 1;

FIG. 4 is a front view of another embodiment of the printed wiring boardused in the present invention;

FIG. 5 is a perspective view of an embodiment of the zero point slideras well as the slider used for the present invention; and

FIG. 6 is a diagram showing an embodiment of a brush used for thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference numeral 1 designates an input shaft and numeral 2 designatesan output shaft, both being in alignment with their axial centers tothereby constitute a steering shaft. A torsion bar 3 is disposed betweenthe input and output shafts. One end of the torsion bar is fitted in abore 1a formed in the input shaft in its axial direction and fixed by afixing pin 4, and the other end is forcibly inserted in a bore 2a formedin the output shaft 2 in its axial direction. The other end of thetorsion bar may be loosely inserted in the bore 2a and may be fixed by afixing pin.

Numeral 6 designates a first housing which is supported by a fixed part(not shown) and which in turn supports the input shaft 1 through abearing 8. Numeral 7 designates a second housing which is connected tothe first housing 6 by means of fitting screws 10 and supports theoutput shaft 2 through a bearing 9.

Numeral 11 designates a slip ring holder made of a resinous materialwhich is firmly connected to the input shaft 1 and is provided with aflange 11a at one end portion thereof. Numeral 12 designates a pluralityof slip rings embedded in the holder 11, each of the slip rings having aconnecting line 13 extending to the side of the flange 11a.

Numeral 14 designates a printed wiring board in a circular plate formfirmly attached to the flange 11a of the holder 11.

FIG. 2 shows the printed wiring board in detail. The printed wiringboard is generally in an annular form and is provided with a cut portion14a at the inner circumferential portion which allows each of theconnecting lines 13 to pass therethrough and a pair of cut portions 14bformed at the outer circumferential portions in an opposing relation toallow determination in position of the printed wiring board. On onesurface of the printed wiring board 14, there is formed elements 15 forconstituting a potentiometer. Namely, numeral 15a designates aresistance layer extending in the circumferential direction of theprinted wiring board 14, which has an electrode 15b at one end extendedin the circumferential direction and another electrode 15c at the otherend which opposes the electrode 15b at a radially outer position. Anoutput electrode 15d is provided opposing the resistance layer 15a at aradially inner position.

The printed wiring board 14 is also provided with an amplifying circuitand a regulation circuit (not shown) for the output electrode 15d.

Referring to FIG. 1, a slider 16 is attached to a surface of a fittingring 17 made of insulating material which is fitted to the outerperiphery of the output shaft 2 and fixed by a fitting screw 18. Theslider 16 is so formed as to extend in the radial direction of theprinted wiring board 14 so that it electrically contacts with both theresistance layer 15a and the output electrode 15b, it having contactingareas with a small width to contact with them.

FIG. 3 shows an embodiment of the slider 16 in detail. The slider 16 ismade of a thin metallic plate having flexibility, a low frictionalcoefficient and good electric conductivity. The slider 16 has a radiallyextending end portion from which a plurality of thin tongue portions asfirst contacting pieces 16a extend in the circumferential direction ofthe printed wiring board so that each end of the contacting pieces 16ais in contact with the resistance layer 15a, and another radially andinwardly extending end portion from which a plurality of thin tongueportions as second contacting pieces 16b extend in the same direction asthe first contacting pieces 16a so that each end of the secondcontacting pieces 16b is in contact with the output electrode 15d.

Turning to FIG. 1, a brush device 19 is formed by a brush holder 20 madeof a resinous material and attached to the first housing 6 and aplurality of brushes 21 each made of a thin wire of an alloy havingflexibility, a low frictional coefficient and good electricconductivity. Each free end is in slide-contact with each of the sliprings 12 and the rear end is fixed to a terminal block 22 embedded inthe brush holder 20. Each of the terminal blocks 22 is connected todrawing wires 24 through each through capacitor 23. The throughcapacitor 23 is to remove noises resulting in the torque detectingdevice due to change in the presence of contact between the brushes 14and the slip rings 12, the change in the contacting pressure causingchange in the resistance of contact whereby external noises are easilygenerated.

Numeral 25 designates a cover for covering the brush holder 20.

Operation of the torque detecting device of the above-mentionedembodiment will now be described.

When a steering wheel is not operated and therefore, no differenceexists in the torque between the input and output shafts 1, 2, there isno displacement in the torsion bar 3. Accordingly, the slider 16 is atthe neutral position in its circumferential direction with respect tothe resistance layer 15a as the element 15 of the potentiometer, wherebyno output results from the potentiometer due to a change in displacementof the torsion bar.

When the steering wheel is operated, there produced a difference intorque between the output and input shafts 1, 2, and there appears adisplacement due to torsion in the torsion bar 3. As a result, theposition of contact of the slider 16 relatively changes in the turningdirection with respect to the resistance layer 15a in proportion to thedegree of displacement in the torsion bar, whereby an output signal isproduced from the potentiometer in proportion to the quantity ofdisplacement. Depending on the direction of turning of the steeringwheel to the left or the right, the position of contact of the slider 16in the circumferential direction of the printed wiring board 14 withrespect to the neutral position of the resistance layer 15a is changedon one side or the opposite side. Accordingly, the direction of rotationto be applied to the output shaft 2 is determined depending on a signaldetected.

In the above-mentioned embodiment, the slip rings 12 and the printedwiring board 14 are mounted on the input shaft 1, and the slider 16 ismounted on the output shaft 2. However, these parts may be substitutedfor attachment to the input and output shafts.

Thus, in the above-mentioned embodiment, the printed wiring boardprovided with the resistance layer and the electrodes which constitute apotentiometer, and the slip rings to transmit signals from theelectrodes to the outside are mounted on either one of the input andoutput shafts, and the slide is mounted on the other one, the sliderextending in the radial direction to contact with the resistance layerand the output electrode of the printed wiring board. Accordingly, theentire construction of a signal detecting assembly for the steeringtorque detecting device can be simple and small-sized.

FIGS. 4 and 5 show another embodiment of the steering torque detectingdevice according to the present invention. In FIGS. 4 and 5, the samereference numerals as in FIGS. 1-3 designate the same or correspondingparts, and therefore, description of these parts is omitted.

As shown in FIG. 4, a zero point detection unit 26 is formed at asymmetric position to the potentiometer 15 with respect to an X--X line.Namely, the zero point detecting unit 26 is formed in a space remainingunutilized on the surface of the printed wiring board 14. The zero pointdetecting unit 26 comprises a zero point electrode 26a having acircumferentially extending end, a zero point contact part 26b having asmall width extended radially and inwardly on the printed wiring board14, and a corresponding electrode 26c which is formed at the innercircumferential side to face the zero point contact part 26b with aspace. The electrode 26a and the corresponding electrode 26c arerespectively connected to the slip rings 12 through the connecting lines13.

FIG. 5 shows a zero point slider 27 made of the same material as theslider 16 which is formed on the surface of the fitting ring 17 on whichthe slider 16, as described with reference to FIG. 3 is formed. The zeropoint slider 27 has a portion in which a plurality of contacting pieces27a are extended in the circumferential direction of the fitting ring 17so that each end of the contacting pieces 27a is in contact with thezero point contact part 26b when the fitting ring 17 and the printedwiring board 14 are assembled to the steering torque detecting device.The zero point slider 27 has another portion in which a plurality ofcontacting pieces 27b are formed to extend in the same direction as thecontacting pieces 27a so that each end of the contacting pieces 27b isin contact with the corresponding electrode 26c when the fitting ring 17and the printed wiring board 14 are assembled.

The position of the zero point slider 27 is so determined so as to be incontact with the zero point contact part 26b only when the difference inthe torque between the input and output shafts 1, 2 is zero, namely,when there is no displacement in the torsion bar 3. When a slightdifference in torque results so that displacement in rotation at a smallrotation angle a is produced, the slider 27 is deviated from the zeropoint contact part 26b, whereby a zero point detecting signal indicatingthat there is a torque in the steering wheel is interrupted.Accordingly, the width of the zero point contact part 26b is made assmall as possible in order to increase accuracy to detect the zeropoint. Namely, it is desirable that the zero point contact part 26bshould be in a linear form in the radial direction.

In operation of the above-mentioned embodiment, when the steering wheelis not operated, and therefore there is no difference in torque betweenthe input and output shafts 1, 2, any displacement of torsion isproduced in the torsion bar 3. Accordingly, the slider 16 is at theneutral (middle) position in the circumferential direction of theprinted wiring board with respect to the resistance layer 15a as anelement of the potentiometer 15, and there is no output from thepotentiometer.

Since the zero point slider 27 extends to contact both the zero pointcontact part 26b and the corresponding electrode 26c, and a signalindicating that there is conduction between the both elements 26b and26c is produced and is detected as the torque zero point for thesteering wheel, the torque zero point signal prevents the motor fromdriving the steering wheel.

When the steering wheel is operated to cause a difference in torquebetween the input and output shafts 1, 2, there is produced adisplacement in the torsion bar 3. Then, the position of the slider 16in contact with the resistance layer 15a is relatively changed by arotating movement in proportion to a quantity of displacement in thetorsion bar, whereby an output signal is generated from thepotentiometer in proportion to the quantity of displacement.

By the change in position of the slider 16, the zero point slider 27becomes out of contact with the zero point contact part 26b due torelative movement in the circumferential direction, whereby anelectrically conducting condition between the corresponding electrode27c and the slider 27 is broken; thus, steering torque is detected. Atthe same time, the condition of preventing the motor from driving forpower steering is released.

Thus, the position of contact of the slider 16 with respect to theneutral position to the resistance layer 15a is changed in thecircumferential direction by the operation of the steering wheel eitheron the left hand or the right hand, whereby the direction of rotation tothe output shaft 2 is determined by the change in the value of thedetected signal.

The above-mentioned embodiment eliminates a problem that, as seen in ananalogical detecting method in the conventional potentiometer,resistance in the resistance layer is not always uniform over its entirearea because the ambient temperature changes, this causing zero pointdrifting resulting in an inconsistency between the zero point in thesteering torque and the zero point of the torque detecting device.

Further, in the above-mentioned embodiment, the zero point sliderextending in the radial direction to contact the zero point contact partof the zero point electrode and the corresponding electrode is mountedon either the input shaft or the output shaft as well as the sliderwhich spans the resistance layer and the output electrode on the printedwiring board. Accordingly, the entire construction of the torquedetecting assembly becomes simple, small-sized and reduces the weight.In addition, correct detection of the zero point in steering torque canbe obtained to thereby improve performance of a power steering system.

FIG. 6 is a front view of an embodiment of the brush used for the torquedetecting device according to the present invention. Reference numeral22 designates a terminal block attached to the brush holder 20 as shownin FIG. 1, and numeral 21 designates a brush made of nickel or a nickelseries alloy and which is formed by a pair of elongated bodies 21a, 21b.Each end of the elongated bodies 21a, 21b is electrically andmechanically connected to the terminal block 22 and the free endsthereof are in contact with a slip ring so as to hold it therebetween.

The reason why the nickel or the nickel series alloy is used for thebrush is to eliminate drawbacks in a conventional flat-plate-like brushmade of phosphor bronze which is generally used for steering torquedetecting devices, is as follows: (a) it rapidly wears because itcontains copper, (b) the manufacturing cost is high, (c) a uniformpressure of contact can not be provided, (d) it has a low durability,and (e) therefore, reliability in its performance is low.

In the brush 21 consisting of two thin elongated bodies 21a, 21b whichhold the slip ring 12 rotated with the input shaft 1 therebetween, evenwhen one elongated brush element becomes faulty due to wear, the otherbursh element normally operates to detect signals.

The pressure of contact of the brush 21 to the slip ring 12 can beadjusted, for instance, by changing the distance between the terminalblock 22 fixing the brush elements 21a, 21b and the slip ring 12.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

We claim:
 1. A steering torque detecting device, comprising:a steeringshaft consisting of an input shaft and an output shaft, a torsion barprovided between said input shaft and said output shaft, a torquedetecting unit for converting a quantity of torsion produced in saidtorsion bar into an electric output, an electricity collecting unitcomprising a slip ring holder connected to said input shaft and having aflange, a plurality of slip rings mounted on said slip ring holders andincluding a connecting line extending to a side portion of said flange,a potentiometer mounted on said side-portion of said flange of said slipring holder, a plurality of brushes which receive said electric outputand supplies electric power from a power source; a plurality of bearingsfor supporting said input and output shafts on the same axial line; anda housing supporting said bearings, wherein each of said brushescomprises a pair of elongated bodies made of nickel or a nickel seriesalloy, a first end of each of which are electrically and mechanicallyconnected to a terminal block of a brush holder and a second end of eachincluding free ends respectively in contact with one of said slip rings.